The present invention relates to fibrous-material grinding apparatus of the kind which includes a housing which incorporates at least one material inlet and at least one material outlet, rotatable grinding device of substantially cylindrical configuration mounted in said housing, and a plurality of stationary grinding devices disposed around the rotatable grinding device and capable of being pressed towards the rotatable grinding device and which together form a grinding gap in which the fibre material is worked and transported from material inlet to material outlet as a result of rotation of the rotatable grinding device.